1. Technical Field
The invention concerns an arrangement for branching a telecommunications cable containing several stranded elements with optical fibers, where at least one stranded element is cut, the optical fibers of the stranded element are spliced to the optical fibers of a branch line, and the branched area is protected with a sleeve.
2. Description of the Prior Art
Most of the existing fiber-optic networks of telecommunication companies comprise point-to-point connections insofar as access to the individual optical fibers is not required. However, new offerers in the telecommunications market such as e.g. supply enterprises, railroad companies, municipal utilities etc. need to access the individual optical fibers because at the time the cables are laid it is not known when and where another subscriber must be connected after the cables have been installed. The possibility of obtaining access to an individual optical fiber after the cable installation must therefore be provided, without impairing any other active optical fiber i.e. one via which information is already being transmitted.
The architecture of such networks is normally an annular structure which needs not necessarily to be a closed one. This means that the optical fibers are looped at or in the vicinity of the subscriber.
The Raychem Company has developed a sleeve for access to the individual optical fibers which can be obtained in the market under the trade name FIST.
In a first application of this sleeve, the cable is cut, a predetermined length of the cable jacket and any central strength element, if present, is removed and the optical fibers of both cables as well as the cable ends are inserted through openings in the bottom part of the sleeve which has the shape of a hooded sleeve. The optical fibers are spliced to each other and are individually placed into cassettes. If one or several subscribers must already be connected when the sleeve is being produced, the optical fibers provided for the connection are spliced to the optical fibers of the subscriber cable. The cables that were inserted through the bottom part are permanently sealed inside the openings.
According to another solution, a predetermined length of the jacket and the central element are removed and the uncut optical fibers are inserted through an oval opening in the bottom part of the hooded sleeve. This requires bending the optical fibers which can cause a breakage of the sensitive optical fibers. In this case as well, the excess lengths of the individual optical fibers are placed into separate cassettes.
Both solutions require that each bared optical fiber must be threaded through a small plastic tube at the installation site to protect it against mechanical damage. This is a time-consuming operation which makes the production of a sleeve at the installation site considerably more expensive. Another disadvantage of these sleeves is that they can only be incorporated during the initial installation, a subsequent incorporation is not possible.